Right now, with Henderson and Wijnaldum having poor seasons
I agree with your post, except for this part, as I'm not sure why those two are singled out. Can has been just as hit & miss for me.
I'd say Henderson, Can and Wijnaldum are all having patchy seasons. Some really good games individually, some poor games.
But all three will benefit more when the balance of the midfield is right, as you say above.
Put a Milner (or Lallana or Ox or Coutinho) in CM, who isn't scared to support the wide players, get forward and create. That allows Wijnaldum, Henderson & Can to do what they do best, offer the energy, breaking up playing and giving the control in games.
The problem with the other three together is I don't think Wijnaldum or Can, when played ahead of Henderson know who is meant to be the more attacking player. They're probably both expected to take the initiative, but it ends up neither do. Then Henderson probably feels he has to force things. When his priority should be to be disciplined and doing the ugly stuff, keeping it fairly simple in possession.
I'll be a bit disappointed if it's that same three against Spurs. However it is far more likely to work against Spurs than it did against United. As Spurs will attack us, so the need to have a creative spark in CM will be less. When it is essential against those sides that sit deep.
I watched Milner's performance back mid week, I think he was really impressive. What I most liked was his clever use of the ball and supporting runs, something our side have lacked without Lallana.